Whenever you see the phrase "what percent" in a question, immediately write down x/100. In this instance, you are going to have two fractions, x/100 = $4.50/ $6.00.
Next you cross multiply. $6x = $4.50 x 100
This simplifies down to 6x =450. Divide both sides by 6 and you get 75. This means 4.5 is 75% of 6.
I hope this helps! Good Luck!